It’s not easy to study the brain during orgasm. “A brain scanner like fMRI is the least sexy place in the world,” says Nan Wise at Rutgers University in Newark, New Jersey. “It’s noisy, claustrophobic and cold.” There is also the problem of keeping your head still – movement of little more than the width of a pound coin can render data useless.

Despite these hurdles, Wise and her colleagues recruited 10 heterosexual women to lay in a fMRI scanner and stimulate themselves to orgasm. They then repeated the experiment but had their partners stimulate them.

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Wise’s custom-fitted head stabiliser allowed the team to follow brain activity in 20 second intervals to see what happens just before, during, and after an orgasm.

Pain relief

Back in 1985, Wise’s colleagues Beverly Whipple and Barry Komisaruk, both at Rutgers, discovered that, during self-stimulation and orgasm, women are less likely to notice painful squeezing of a finger, and can tolerate more of this pain. They found that women’s ability to withstand pain increased by 75 per cent during stimulation, while the level of squeezing at which women noticed the pain more than doubled.

Now Wise’s team has explained why. At the point of orgasm, the dorsal raphe nucleus area of the brain becomes more active. This region plays a role in controlling the release of the brain chemical serotonin, which can act as an analgesic, dampening the sensation of pain.

Her team also saw a burst of activity in the nucleus cuneiformis, which is a part of brainstem systems that are thought to help us control pain through thought alone.

“Together, this activity – at least in part – seems to account for the pain attenuating effect of the female orgasm,” says Wise.

Turn on, not off

In 2005, Gert Holstege at the University of Groningen in the Netherlands used a PET scanner to analyse brain activity in 13 women while they were resting, faking an orgasm and being stimulated by their partner to orgasm. While activity in sensory regions of the brain increased during orgasm, activity fell in large number of regions – including those involved in emotion – compared with their brain at rest.

Based on this finding, it was suggested that women have to be free from worries and distractions in order to climax. From an evolutionary point of view, the brain might switch off its emotional areas because the chance to produce offspring is more important than the immediate survival to the individual.

But the new study saw the opposite: brain activity in regions responsible for movement, senses, memory and emotions all gradually increased during the lead-up to orgasm, when activity then peaked and lowered again. “We found no evidence of deactivation of brain regions during orgasm,” says Wise.

The difference between the two studies may be because PET can only get a small snapshot of brain activity over a short period of time, unlike fMRI scanners.

Better understanding

It’s not yet clear why pain sensation decreases during orgasm, or if men experience the same phenomenon. It may be that, in order to feel pleasure in the brain, the neural circuits that process pain have to be dampened down.

Whipple suggests that the pain-dampening effects of the female orgasm could be related to child birth. Her research suggests that pain sensitivity is reduced when the baby’s head emerges through the birth canal. Vaginal stimulation may therefore reduce pain in order to help mothers cope with the final stages of birth, and promote initial bonding with the baby.

The ability to study what happens during stimulation and orgasm could be used to better understand and treat those who have mood disorders like anhedonia – the inability to experience pleasure, says Wise. “We know so little about pleasure in the brain, we are just now learning the basics.”

You might wonder what it’s like to participate in such experiments. Wise says people often think her participants must be exhibitionists, but it’s not the case, she says. “Some women do like that aspect, but most are doing it because it’s empowering to them. Some find it difficult to orgasm, others don’t. One of our participants in this experiment was a 74-year-old lady who had two fabulous orgasms in the machine. I said to her, ‘You go girl!’ ”